Onychomycosis due to rhizomucor in psoriatic patient with HIV infection.

Onychomycosis is frequently seen in dermatological clinical practice worldwide. The causative agents are usually two pathogenic groups of fungi namely, dermatophytes and yeasts of the genus Candida. In some cases, non-dermatophytic molds belonging to different genera and species may be the etiological agents. We report an unusual case of onychomycosis in an HIV-positive psoriatic patient caused by Rhizomucor pusillus, which has not been mentioned in the literature before. Our finding underline the fact that fungal species appearing as contaminants should be evaluated by proper clinical-mycological correlation to ensure an accurate diagnosis.

What was known?

Dermatophytes, yeasts, and moulds are all potential causes on onychomycosis worldwide. Often, non-dermatophytes are considered contaminants or secondary pathogens in onychomycosis, invading the already damaged by trauma or disease.

Introduction

Onychomycosis is a frequent clinical entity encountered in dermatological practice worldwide. Accounting for about 50% of nail infections, its incidence is rising owing to a number of factors including an ageing population and expanding number of immunocompromised patients.[1] The clinical picture is characterized by alterations in nail architecture like changes in color, thickness, onycholysis, and onychodystrophy. [2] The main types are distal and lateral subungual onychomycosis, superficial onychomycosis, proximal subungual onychomycosis, endonyx onychomycosis, and total dystrophic onychomycosis. In addition, patients may show different combinations of these patterns.[3] Although not life-threatening, patients with onychomycosis suffer from serious physical, psychosocial, and occupational effects. Most commonly, onychomycosis is caused by various species of filamentous fungi like the dermatophytes or yeasts of the genus Candida. However, non-dermatophytic molds with known habitats mostly in soil and decaying plant debris are now being increasingly recognized as pathogens in fungal nail infection. Prevalence rates of onychomycoses caused by non-dermatophyte molds range between 1.45% and 17.60%. The most common non-dermatophytes molds causing nail disease are Scopulariopsis, Scytalidium, Fusarium, Aspergillus, and Onychocola canadensis.[4] Onychomycosis due to dermatophytes and non-dermatophytes is clinically indistinguishable, hence underlining the need of relevant laboratory investigations before starting the treatment.

Case Report

A 35-year-old man, laborer by occupation, presented with discolored and thickened fingernails of both the hands. He gave a history of loss of weight for the past 1 year and development of multiple crusted to scaly, erythematous papules and plaques all over the trunk, both arms, and lower limbs. There was extensive scaling of the scalp also. Mild itching was associated with the skin lesions. About 2-3 months after the appearance of skin lesions, he noticed discoloration and brittleness of the nail of little finger of the left hand. Gradually, the rest of the finger nails of both the hands got involved. General examination revealed thin, cachexic build of the patient. Cutaneous examination revealed hyperpigmented macules, scaly erythematous papules, and few lichenoid plaques with adherent scales diffusely present over the trunk and extremities. The fingernails showed yellowish discoloration, subungual hyperkeratosis, and pitting shown in clinical Figures 1 and 2. With this clinical history and physical examination, possibility of underlying immunosuppression was contemplated. The patient was advised for HIV testing, which revealed that he was HIV-positive. It was found that his CD4+ count was 118/mm3. He was started on anti-retroviral therapy (ART) at the ART clinic and referred back to the dermatology department for management of skin lesions. Further, he was sent for histopathological investigations, which demonstrated psoriasiform hyperplasia of the epidermis, focally diminished granular layer, suprapapillary thinning and congested vessels in the dermis. The PAS stain for fungal hyphae was negative. Nail clippings and subungual debris were taken for mycological examination. KOH examination of the scrapings revealed wide, ribbon-like hyphae typical for Zygomycetae. The nail clippings were seeded on Sabouraud dextrose agar. There was a rapid growth seen in two days, which filled the tube. The colony was woolly, white initially and turned gray with time. The reverse was white to pale. Slide culture revealed non-septate broad hyphae with internodal rhizoids, irregularly branched sporangiophores with sporangia at their apices. Sporangia were brown in color and round in shape. Apophysis was absent. Columellae were prominent and spherical to pyriform in shape. Sporangiospores were small, unicellular, and round in shape. The isolate was able to assimilate sucrose. The diagnosis of Rhizomucor pusillus was made. After the first diagnosis, a second sample was taken, the laboratory procedures were repeated, and the diagnosis was confirmed. Clinician dermatologists were informed about the diagnosis, and the patient was started on fluconazole. The patient did not return for therapeutic success evaluation.

Figure 1

Showing lesions on toe nails

Figure 2

Showing lesions on finger nails

Discussion

The class Zygomycetes includes the order Mucorales, which contains the genus Rhizomucor. It is a saprophytic fungi, found in soil and decaying vegetation and isolated from environmental sources worldwide. Rhizomucor is a rare cause of human disease and occurs as an opportunistic infection. Limited available in vitro susceptibility testing demonstrates R. pusillus susceptibility to amphotericin B but resistance to flucytosine, fluconazole, miconazole, and ketoconazole. Only 6 of the 19 patients with Rhizomucor infection described in the literature have responded to treatment. However, there has been no known case report on onychomycosis caused by Rhizomucor species.[56] In our patient, ribbon-like hyphae in direct KOH mount and microscopic morphology of the cultured fungus consistent with Rhizomucor was found. Same findings obtained on mycological investigations conducted on two different occasions in the absence of dermatophyte growth suggest that Rhizomucor is the causative agent of nail disease in this patient.

The prevalence of onychomycosis is dependent on various host factors. It is seen to be higher in patients with an HIV infection.[5] Preceding nail trauma predisposes to non-dermatophyte-mold onychomycosis. Dystrophic psoriatic nails are easier for the fungi to penetrate as the nail plate is already compromised, hence there is a higher prevalence of onychomycosis in psoriatics compared with non-psoriatics.[7] Our patient was HIV-positive and suffered from psoriasis also. Both these factors could have been involved in the occurrence of fungal nail infection by Rhizomucor, a non-dermatophytic mold. To the best of our knowledge, there has been no data on onychomycosis due to Rhizomucor species, although it has been reported to cause systemic infection in immunocompromised individuals.[68] This unique case report underlines the fact that fungal species appearing as environmental contaminants in the nail samples should be further investigated with suspicion in view of appropriate clinical history and examination. Accurate mycological diagnosis is of utmost importance in the correct management of onychomycoses.

What is new?

Non-dermatophytic molds must be kept as one of the differential diagnosis while investigating and treating a case of onychomycosis and the common practice of discarding them, considering them to be contaminants should be avoided. Regarding laboratory diagnosis, it is extremely important to confirm if the fungus is real etiological agent by repetition of the tests on a new collected sample.